To cope with increase in information transmission amount, recent electronic devices and the like often employ opto-electric hybrid boards which include electric wiring as well as optical wiring and are capable of simultaneously transmitting electrical signals and optical signals. As shown in FIG. 7, a known opto-electric hybrid board includes, for example, an electric circuit board E including an insulation layer 1 such as of a polyimide serving as a substrate and an electric wiring 2 of an electrically conductive pattern provided on a front surface of the insulation layer 1, and an optical waveguide W provided on a back side of the electric circuit board E and optically coupled to an optical element mounted at a predetermined position on the electric wiring 2. A front surface of the electric circuit board E is protected with a cover lay 3 for insulation thereof. The optical waveguide W has a triple-layer structure including an under-cladding layer 6, a core 7 serving as an optical path, and an over-cladding layer 8.
The opto-electric hybrid board 10 may be mounted as it is in an electronic device, or may include an opto-electric connection ferrule attached to a distal end portion thereof for use as a connector for connection between a plurality of boards or between chips provided on a board.
Where a component such as the ferrule is attached to the opto-electric hybrid board 10, it is important to accurately position the component with respect to the opto-electric hybrid board 10 so as to prevent an optical loss. Therefore, the core 7 serving as the optical path needs to be accurately positioned with respect to the outline of the opto-electric hybrid board 10. Accordingly, the outline of the opto-electric hybrid board 10, particularly an end face of the opto-electric hybrid board 10 to be connected to the component, should be processed with higher dimensional accuracy.
Where the optical waveguide W per se is used as an optical connector, the outline processing of the optical waveguide W requires higher accuracy for the same reason as the outline processing of the opto-electric hybrid board 10. To meet this requirement, an optical waveguide production method for producing the optical waveguide W is proposed, as shown in FIG. 8, which includes the steps of forming an under-cladding layer 6, simultaneously forming a core 7 and outline processing alignment marks 11 from a core material on a surface (a lower surface in FIG. 8) of the under-cladding layer 6, and forming an over-cladding layer 8 over the core 7 on the under-cladding layer 6 (on a lower side in FIG. 8) with the alignment marks 11 uncovered (see PTL 1).
In the aforementioned production method, the core 7 serving as the optical path and the alignment marks 11 are formed on the same basis, so that the alignment marks 11 can be accurately positioned with respect to the core 7. Further, the alignment marks 11 are visible through the transparent under-cladding layer 6 as indicated by arrows in FIG. 8. With reference to the alignment marks 11, therefore, the outline processing operation can be advantageously performed on the optical waveguide W with higher accuracy.